Method of fabricating a detonation squib



Feb- 14, 1967 J. C. KYLE 3,303,737

METHOD OF FABRICATING A DETONATION SQUIB Original Filed April ll, 1963 2 Sheets-Sheet l Feb. 14, 1967 J. c. KYLE 3,303,737

METHOD OF FABRICATING A DETONATION SQUIB Original Filed April l1, 1963 2 Sheets-Sheet 2 26d M l@ Unite taes atet 3,303,737 METHD E" FABRECA'HNG A DETONATIN SQUIB .lames C. Kyle, Glendora, Calif., assigner, by mesne assignments, to Physical Instruments Corp., Los Angeles, Calif., a corporation of California Original application Apr. 1l, 1963, Ser. No. 272,384. Divided and this application Apr. 19, 1966, Ser. No.

9 claims. (ci. se-i) The application isandivision of application Serial No. 272,384, filed April 11, 1963, now Patent Number 3,274,937.

This invention relates to a detonator or squib of the type employed, for example, on aerial Vehicles such as rockets and missiles. Such a detonator contines an eX- plosive charge which is electrically detonated for some useful purpose, for example, to separate two stages of a rocket or missile in response to an electrical signal. Typically, a detonator is a metal fitting adapted to screw into a tapped bore at the location where the explosive force is required, the outer end of the tting being adapted for connection to a control circuit.

The primary requisite is, of course, reliability, since the success of the whole project may depend upon the proper functioning of such a detonator. One kind of reliability to be sought is structural reliability to forestall any possibility of mechanical failure prior to the moment of detonation and to forestall mechanical failure caused by the explosion per se. A second kind of reliability is in the functioning of the firing circuit, it being mandatory that detonation occur only when the firing voltage reaches a precisely predetermined magnitude.

The present invention achieves mechanical reliability by employing a suitably rugged metal body or housing to confine the explosive charge and by mounting the components of the firing circuit in the metal housing in a sealed manner by suitable ceramic material. It has been found that mounting a conductor of the firing circuit in a longitudinal bore of lthe detonator housing by means of a suitable ceramic and then heating the assemblage to a high temperature results in a construction that is not only huid tight, but is also capable of withstanding the maximum force that can be generated by the explosive charge. The high structural strength results from the ceramic material fusing `both to the conductor that it surrounds and to the surrounding metal of the detonator housing.

To make the detonator immune to applied voltages below a desired critical voltage, the detonator incorporates a suitable spark gap formed by two spaced electrodes. The mounting of the circuit components in fused ceramic introduces a problem, however, in that the high temperature processing for the fusing of the ceramic affects the metal surfaces of the two electrodes that form the spark gap.

The invention solves this problem by dividing the detonator into two sections or assemblies which separate at the spark gap, the two electrodes being carried by the two assemblies respectively. This construction makes it possible to re the two assemblies separately to bond the two electrodes by fused ceramic and then subsequently to process the two electrodes to expose clean metal before joining the two assemblies permanently to form the final product.

In the presently preferred practice of the invention, one of the two assemblies includes the detonator housing with the detonation cavity at one end of the housing and the second assembly is in the form of a ceramic insert that telescopes into the detonation cavity to form the inner end of the detonation cavity. With the insert backed against an inner shoulder of the housing and effectively sealed in its assembled position, there is no possibility of the explosion creating a separate force -between the two interconnected assemblies.

For assurance of functional reliability, the spark gap between the two electrodes must be repeatedly tested by applied voltages before the detonator is loaded with explosive. the electrodes are made of the usual metals and insulated from each other by conventional m-aterials including the usual ceramics, it is found that a spark test materially changes the critical breakdown voltage and the repeated pretests required for reliability repeatedly vary the critical voltage usually in a progressive manner.

It is dimcult to identify all of the causes that may exist for changes in the critical voltage in response to preliminary spark tests. It is known that the metal employed for the electrodes may be pitted or otherwise directly affected by the spark discharge. It has also been found that conventional insulation materials including various ceramics employed to form the spark chamber are deteriorated by the spark discharge. The deterioration may contaminate the spark chamber atmosphere and has been observed to form deposits on the electrode surfaces.

With respect to this problem an important feature of the invention is the discovery that employing a particular alloy for the electrodes and employing a particular ceramic to form the spark chamber makes it possible to spark test the detonator in advance any desired number of times without changing the critical voltage at which :sparking occurs.

In some practices of the invention one side of the firing circuit is a grounded side which includes the detonator housing. In the embodiment of the invention selected for the present disclosure, however, two insulated conductor means incorporated in the detonator construction form the opposite sides of the ring circuit.

Briefly described, the preferred procedure for fabricating this embodiment of the invention is as follows.

A stainless steel detonator housing is provided with a detonation cavity in one of its ends and a receptacle cavity in the other end for use in connecting the detonator to a firing circuit. Two longitudinal bores interconnect the two cavities, and a pair of identical electrode pins with end sockets in their inner ends are mounted in these two longitudinal bores by a suitable ceramic. The detonator housing with the two electrode pins mounted therein is what may be termed the first assembly, and this assembly is suitably tired at a high temperature to fuse the ceramic both to the electrode pins and to the housing.

A second pair of shorter electrode pins of substantially smaller cross section than the end sockets of the first electrode pins are designed to telescope into the end sockets. One of the shorter pins is crimped to increase its effective cross section for frictional t into the corresponding end socket of the corresponding longer electrode pin. The other shorter electrode pin is coated with ceramic of a thickness for snug tit into the end socket of the second longer electrode pin. After this coating is fired for fusion, it is cut away to leave two ceramic sleeves separated by a circumferential gap where the metal of the smaller electrode is exposed.

The two shorter pins are then mounted in a ceramic body to form what may be termed the second assembly, which serves as an insert for insertion into the detonation A serious difficulty is encountered in that/'ifV d cavity of the first assembly -to form the bottom of the detonation cavity. When the second assembly is inserted in this manner, the two shorter electrode pins carried by the second assembly mate with the end sockets of the longer electrode pins of the rst assembly. The two assemblies are then cemented together.

At this point the spark gap may be tested as many times as desired by applying a rising voltage across the spark gap to note at what point sparking occurs. `If the results are consistent as required, the final step is to load the detonation cavity with explosive and then to seal the cavity in the usual manner.

The various features and advantages of the invention may be understood from the following detailed description together with the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative FIG. 1 is a longitudinal sectional View of the selected embodiment of the invention;

FIG. 2 is an enlarged fragment of FIG. 1;

FIG. 3 is a longitudinal sectional View of the detonator body or housing;

FIG. 4 is an elevational exploded view showing how ceramic beads or sleeves may be assembled on the two longer electrode 4pins for the purpose of mounting the longer electrode pins in the detonator housing;

FIG. 5 is a longitudinal sectional view of the rst assembly comprising the detonator housing with the two longer electrode pins permanently mounted therein;

FIG. 6 is a longitudinal sectional view of the second assembly ready for insertion into the first assembly;

FIG. 7 is a sectional view illustrating a step in the fabrication of the second assembly or insert;

FIG. S is a sectional view showing a later step in the fabrication of the second assembly or insert; and

FIG. 9 is a View partly in section and partly diagrammatic illustrating the manner in which the detonator may be electrically tested a number of times in advance of the loading of the detonator with explosive.

In FiIG. 1 showing a completed detonator, a detonator body or housing 10 made of stainless steel is formed with an external screw thread 12 and a hexagonal flange 14 to permit the housing to be screwed into a tapped bore where the explosive force is required. The inner end of the detonator housing 10 is formed with a longitudinal detonation cavity 15 which is filled with an explosive charge 16, and the other end of the housing is formed with what may be termed a receptacle cavity 18 provided with peripheral lugs 20 for connecting the detonator to a firing circuit.

A pair of longitudinal bores 22 extend from the detonation cavity 1-5 to the receptacle cavity 18 and are occupied respectively by a first pair of relatively long electrode pins 24 and 25 which protrude into the receptacle cavity 18 for electrical connection to the two sides of a firing circuit. The two long electrode pins 24 and 25 are mounted in the two longitudinal bores by means of sleeves 26 of ceramic material which are fused both to the electrode pins and to the surrounding walls of the longitudinal bores. The receptacle cavity 1S has an insulating ceramic layer 28 across its inner end and is further provided with an O- ring 30 to make the electrical connection fluid tight. The detonation cavity 15 is sealed by means of an inner gasket 32 and an outer metal disk 34 which is welded to the detonator housing.

A second shorter pair of electrode pins 35 and 36 are mounted in a ceramic insert which has a peripheral cylindrical wall 42 of stainless steel that is bonded by ceramic cement to the surrounding wall of the detonator housing 10. The inner ends of the two short electrode pins 35 and 36 are interconnected by an explosive wire 44 in a well-known manner, the explosive wire being welded to the two pins and extending yacross an axial cavity 45 of the ceramic insert, this cavity being provided for a shaped charge effect.

The inner ends of the two longer electrode pins 24 and 25 extend through an insulating ceramic layer 46, the inner ends being enlarged to form radial shoulders 48 and being further formed with end sockets 50 and 52 respectively to receive the leading ends of the two shorter electrode pins 35 and 36. The leading ends of the two shorter electrode pins 35 and 36 are substantially smaller in cross section than the end sockets into which they t. The short electrode pin 36 is crimped or offset as shown to increase its effective cross section to fit snugly into the end socket 52 for the purpose of electrically connecting the .short electrode pin 36 with the corresponding longer electrode pin 25. As best shown in FIG. 2, the short electrode pin 35 is provided with a ceramic coating to make it fit snugly into the end socket 50 of the corresponding longer electrode pin 24. nThe ceramic coating is interrupted by a circumferential gap 54 whereby the ceramic coating is separated into two axially spaced ceramic sleeves 55a and 55h.

It is apparent that when a rising voltage is applied across the two longer electrode pins 24 and 25, a firing circuit is formed through the explosive wire 44 with the circuit broken by the circumferential gap 54 where a radial air space separates the short electrode pin 35 from the surrounding wall of the corresponding longer electrode pin 24. When the voltage rises to a predetermined magnitude, the firing circuit is closed by a spark across this radial gap to ignite the explosive wire 44.

Any explosive force that gets past the ceramic insert 40 to reach the inner ends of the two long electrode pins 24 and 25 is successfully withstood because of the effectiveness with which the two long electrode pins are bonded to the surrounding detonator housing 10. 1n this regard, it is to be noted that the interface between each of the long electrode pins and the wall of the surrounding longitudinal bore is of substantial area and longitudinal dimension for exceedingly high strength. It is also to be noted that the interface between each of the long electrode pins and the surrounding ceramic material is also extensive, and in addition the radial shoulder 43 of each long electrode pin backs against the ceramic material in positive engagement therewith.

Method of fabrication As heretofore indicated, an important feature of the invention is the discovery that using electrodes of a particular alloy in combination with a ceramic material made of a particular mixture results in a spark gap chamber in which sparking creates no deterioration whatsoever and any number of preliminary sparking tests may be conducted without affecting the breakdown voltage at which sparking occurs. The electrode alloy is Inconel 600, which may analyze, for example, approximately 77.60% nickel, 15.57% chromium, 6.38% iron, 0.21% manganese, 0.14% silicon, and 0.02% carbon.

The ceramic material is prepared in three stages. The rst stage employs a mixture A comprising the following materials in parts by weight:

This mixture which melts at 1480 to 1520 F. is smelted in a covered Crucible at approximately 1800 F. until it is homogenized. The smelt is then quenched in water and thereafter is wet ground and passed through a suitable screen such as a 400 mesh screen.

The second stage employs the following mixture B:

Percent Li2CO3 8.06 Na2C03 19.40 A1203 0.74 H3B03 19.10 Ti02 2.60 Si02 49.00 C0304 1.10

Mixture B is processed in the same manner as mixture A to result in a finely divided product.

The third stage consists in mixing the products of mixtures A and B in equal parts by weight and smelting to produce a homogeneous product which is cooled and ground to a fine powder. This final powder product may be used in any suitable manner to form the ceramic sleeves 26 of FG. 1 that bond the two long electrode pins 24 and 25 in their assembled positions in the detonator housing 10.

In the preferred practice of the invention, the ceramic material is molded into beads or sleeves of appropriate dimensions for mounting the two long electrodes in the two longitudinal bores 22. Thus, FG. 4 shows three ceramic beads or sleeves 26a dimensioned to lit over the enlarged end portion of each of the two electrode pins 24 and 25, and FIG. 4 further shows two longer beads or sleeves 26h molded from the ceramic material and dimensioned to tit over the portion of the electrode pin that is of smaller diameter.

Both the detonator housing and the two electrode pins 24 and 25 are preoxidized by exposure in a furnace for ten minutes, at 1560 F. to create oxide coatings with which the ceramic material will fuse in a highly effective manner. The ceramic beads or sleeves 26a and 26h are then telescoped over the two electrode pins 24 and 25, and the electrode pins are placed in their assembled positions in the two longitudinal bores 22. The assembly is then tired at 1850 F. for 25 minutes. When the assembly cools down, it is found that the ceramic material forming the ceramic sleeves 26 shrinks in the two bores 22, as may be seen in FIG. 1. The assembly is then tested for leaks along the bores 22 and is additionally tested for the dielectric strength of the ceramic sleeves 26.

The next step is to install the ceramic layer 28 in the bottom of the receptacle cavity 18. First, polyvinyl masking sleeves (not shown) are telescoped over the exposed ends of the two electrode pins 24 and 25, with the masking sleeves terminating short of the bottom of the cavity in accord with the desired thickness of the layer 2S. The ceramic layer 28 comprises 40% by weight .of the same ceramic material as the ceramic sleeves 26 and 60% thermosetting epoxy known as Helix R-385 produced by Carl H. Biggs Company, 1547 Fourteenth Street, Santa Monica, California. After the layer 28 is applied, the masking sleeves are removed from the electrode pins, and the assembly is placed in an oven at 180 F. fortwo hours to cure the layer.

The next step is to apply the sealing layer 46 at the inner ends of the electrode pins 24 and 25, which layer may be of the same composition as the layer 28. Since allowance must be made for shrinkage, the layer 46 initially extends beyond the pins of the electrode pins 24 and 25; but after an oven cure of 180 F. for two hours, the layer shrinks. A flat bottom drill is then rotated by hand in the detonation cavity to remove the excess material and reduce the layer 46 to a thickness that is Hush with the inner ends of the two electrode pins 24 and 25.

The various heat treatments, and especially the step of tiring the ceramic sleeves 26, results in oxidation of the exposed portions of the two electrode pins 24 and 25. These effects are remedied by rst using a 60 countersinking tool to chamfer the rims of the end sockets 50 and 52 of the two electrode pins 24 and 25, and then a drill in a pin vise is employed to drill out the two end sockets to remove the oxides formed therein. The bottoms of the sockets are then reamed out, and all chips are removed by using jets of dry nitrogen. This operation completes the fabrication of the first assembly, which is shown in its completed form in FIG. 5.

The next step is to coat a short electrode pin with ceramic in preparation for the fabrication of the second assembly or ceramic insert 40. In practice, a number of the short electrode pins 35 are mounted by their base portions in a suitable fixture and are sprayed uniformly with the ceramic powder constituting the previously described mixtures A `and B, to 45% yof the spray mixture being water. The coating may be sprayed to a thickness, for example, of approximately 0.04 inch. The sprayed pins are placed in an oven for one hour at 350 F. and then are placed in a furnace for 71/2 minutes to fuse the ceramic coating to the pins. The furnace is raised to a temperature of 1455 F. and then de-energized when the pins are inserted. The lfixture carrying the coated pins is mounted on a nickel plate that serves as a heat sink, the nickel plate being preheated to furnace temperature. In addition, the coated pins are covered by a heavy metal cap which is preheated to the previous oven temperature of 350 F. The coated pins are subsequently air cooled without removing the heavy metal cap, and then a blower is employed to cool the coated pins to room temperature. Finally, the coating is dressed to a thickness of 0.0335 inch with the guidance of a shadowgraph.

The body of the ceramic insert 40 comprises the following materials in parts by weight:

This mixture is smelted at 2100 F. to produce a homogeneous mass, which is then quenched and ground to 400 mesh size. With the use of beeswax as a binder, the powdered material is molded to the desired configuration of the previously described ceramic insert 40 with bores for the electrode pins 35 and 36, and then the molded body is heated to 350 F. for 20 minutes to volatilize the beeswax. 'Ilhe molded body is then sintered at 1120 F. for 14 minutes with the molded body standing on one end and then is reversed end to end for an additional firing period of 151/2 minutes. The molded body is then air cooled and subjected to a blower for reduction to room temperature. At this stage, the molded body is small enough in diameter to |fit into the previously mentioned stainless steel cylinder 42, but is appreciably longer than the steel cylinder.

To carry out the next step, a pair of electrode pins 35 and 36 are mounted in a fixture in the manner indicated in FIG. 7, the leading portion of the electrode pin 35 having a ceramic coating and the leading portion of the electrode pin 36 being uncoated. The two electrode pins have at this stage base portions of excessive length to permit adequate support of the electrode pins in the fixture 58.

The molded ceramic block 40a that is eventually to `be the ceramic body of the insert 40 is then slipped into the stainless steel cylinder 42 and is slipped over the erect electrode pins 35 and 36 in the manner shown in FIG. 7. As may be seen in FIG. 7, the molded ceramic body 40a and the surrounding cylinder 42 seat in a circular recess in the fixture 58 with the excess length of the ceramic body extending beyond the upper rim of the cylinder 42. A heavy metal lblock 62 to serve as a weight is provided with a pair of bores 64 to clea-r the leading ends of the two electrode pins 35 and 36. The weight 62 is placed ove1 the two electrode pins as shown in FIG. 7 with the weight resting on `the upper protruding end of the ceramic body 40a.

With an oven heated to la temperature of l350-l375 F. and then de-energized, the assembly shown in FIG. 7 is placed in the oven for ten minutes to cause fusion of the ceramic. Under the pressure exerted by the weight 62, the heated ceramic settles compactly into the cylinder 42 and around the base portions of the two electrode pins 35 and 36 with the excess ceramic extruded by the weight over the upper rim Iof the stainless steel cylinder. When the assembly is removed from the fixture 58, the excess lengths of the base portions of the two electrode pins 35 and 36 are severed, and then the back face of the insert assembly is ground to the desired axial dimension of the assembly. A carbide spade drill is then employed to form the cavity 45 in the ceramic insert.

The final processing of the insert 40 is carried yout in the manner indicated in FIG. 8. The leading ends of the two electrode pins 35 and 36 are inserted through a pad 65 of a suitable elastomer for protection against the effects of Sandblasting. A Teflon sleeve 66 is then placed over the end of the electrode pin 35, with the end of the sleeve spaced from the pad 65 by the width desired for the previously mentioned circumferential spark gap d. The exposed portions of the two electrode pins 35 and 36 are then sandblasted to remove the ceramic coating of the electrode pin 35 between the sleeve 66 and the pad 65 and to abrade the end portion of electrode pin 36 to expose clean metal. The Iremoval of the portion of the ceramic 55 from the electrode pin 35 leaves the two previously mentioned ceramic sleeves 55a and 55b. The leading end of the electrode pin 36 is then crimped to the configuration shown in FIGS. l and 2, and explosive wire 44 is spot welded to the rear ends of the two electrode pins 35 and 36. The two spot welds Iare then tested for mechanical strength, and voltage is applied to test the dielectric around the two electrode pins.

FIG. 6 shows the completed second assembly or insert l0 poised for installation in the first assembly shown in FIG. 5. With the two short electrode pins 35 and 36 aligned with the longer electrode pins 24 and 25, the insert 4f) is advanced into the detonation cavity l5 of the first assembly to the final position of the insert where the two electrode pins 35 and 36 telescope int-o the two corresponding end sockets 50 and 52 of the longer electrode pins 24 and 25. This assembly is placed in an oven at 180 F. for five minutes in preparation for cementing the insert 45 to the surrounding metal of the detonator housing lil.

After the five-minute heating period, the cement comprising the previously described mixture of ceramic and epoxy is applied by means of a hollow needle to form a small fillet around the rim of the stainless steel cylinder 42, such a fillet being indicated at 68 in FIG. 2. The assembly is then `oven cured for four hours 'at 120 F., during which period the cement fillet 65 migrates by capillary attraction over the length of the outer circumference of the stainless steel cylinder 42 for effectively bonding the two assemblies together.

The device as completed to this stage is then suitably tested electrically, for example, by means of a fixture 70, shown in FIG. 9, having two prongs 72 and 74 for electrical contact with the rear ends of the two short electrode pins 35 and 36 respectively. A metal sleeve 75 is placed on the exposed end of the long electrode pin 25, and a circuit 76 is completed between the prong 74 and the metal sleeve '75 for application of voltage to test the electrical continuity between the long electrode pin 25 and the correspondingly short electrode pin 36. A second metal sleeve 78 is placed on the long electrode pin Z4, and a test circuit S0 is :completedbetween the sleeve 78 tand the prong 72 for the purpose lof applying a rising voltage across the spark gap between the electrode pins 24 and 35. If the spark occurs consistently at the desired voltage, the fabrication of the detonator is completed by adding the explosive charge 16 to fill the detonation cavity 15 and iby further applying the gasket 32 and the closure disk 34.

The various ceramic materials that are employed are especially effective for forming bonds with stainless steel surfaces and have thermal coefficients of expansion that are compatible with stainless steel. With the electrode pins made of the specified alloy and with the two ceramic sleeves 55a and 55b made of the specified ceramic material, no deterioration is created by spark tests, and the device may be spark tested any number of times without change in the breakdown voltage at which sparking occurs. The electrodes that form the spark gap are held in position by ceramic fused at a high temperature, but the fabrication of the `device in two separate assemblies, one of which plugs into the other, makes it possible to abrade the electrodes to expose clean metal after the firing operations are carried out.

My description in specific detail of the selected practice of the invention will suggest various changes, substitutions, and other departures from my disclosure within the spirit and scope of the appended claims.

What is claimed is: 1. A method of fabricating a detonation device of the character described, including the steps of:

forming a first electrode with a socket in one end; forming a second electrode of a cross section to telescope into said socket with radial clearance;

mounting the first electrode in a first mass of ceramic material and firing to fuse the ceramic rnass to the electrode to form a first assembly;

mounting the second electrode in a second mass of ceramic material and firing to fuse the second ceramic mass to the second electrode to form a second assembly;

forming a ceramic sleeve on said second electrode for snug fit of the second electrode into said socket with a circumferential gap lin the sleeve;

abrading the second electrode at said gap to expose clean metal;

and then mating the two assemblies with said second electrode telescoped into said socket.

2. A method of fabricating a detonation device of the character described, including the steps of:

mounting a first electrode in a metal housing in an insulated manner by means of ceramic and firing the ceramic to form a first assembly;

mounting a second electrode in a mass of ceramic and firing the ceramic to form a second assembly adapted to mate with the first assembly to form a spark gap between the two electrodes;

mating the two assemblies;

repeatedly applying voltage across the two electrodes to test for the breakdown voltage across the spark gap? and then mounting explosive material in said housing.

3. A method of fabricating a detonation device of the character described, including the steps of:

forming a first electrode with a socket in one end;

forming a second electrode to telescope into said socket with radial clearance;

mounting one of said electrodes in a metal housing by means of ceramic and firing the ceramic to form a first assembly;

mounting the other of said electrodes in a mass of ceramic material and firing to form a second assembly for mating with the first assembly;

forming a ceramic coating on said second electrode to fit into the socket When the two assemblies mate, said coating having a circumferential gap to form an annular Spark chamber when the two assemblies mate;

abrading the second electrode at said gap to expose clean metal;

mating the two assemblies;

repeatedly applying voltage across the two electrodes to test for the breakdown voltage across the spark gap;

and then mounting explosive material in said housing.

4. A method as set forth in claim 3 which includes the step of abrading said socket to expose clean metal before mating the two assemblies.

5. A method of fabricating a detonation device of the character described, including the steps of:

forming a metal housing with a receptacle capity at one end and a detonation cavity at the other end with the two cavities interconnected by `at least one bore; forming a first electrode with a socket in one end; forming a second electrode of a cross section to telescope into said socket with radial clearance; mounting one of said electrodes in said bore by means of ceramic material and firing to fuse the ceramic to make a first assembly; mounting the other of the two electrodes in a mass of ceramic material and firing to form a second assembly for insertion into said detonation cavity to form the inner end of the cavity; forming a ceramic coating on said second electrode to fit into the socket when the second assembly is inserted in the detonation cavity, with a gap in the coating to form an annular spark chamber when the first assembly is inserted into the second assembly;

abrading at least one of said two electrodes to expose clean metal;

inserting the second assembly into the first assembly;

repeatedly applying voltage across the two electrodes to test the breakdown voltage across the spark gap; and then placing explosive material in said detonation cavity.

6. A method of fabrication as set forth in claim 5 which includes the step of bonding the two assemblies together after the second assembly is inserted `into the first assembly.

7. A method of fabricating a detonation device of the character described, including the steps of:

forming a metal housing with a receptacle cavity at with the two cavities interconnected by two longitudinal bores;

forming a first pair of electrodes with a socket in one end of each electrode;

forming a second pair of electrodes to telescope into said sockets with radial clearance;

mounting one of said pair of electrodes in said two bores by means of ceramic material and firing to fuse the ceramic to make the first assembly;

mounting .the other of said pairs of electrodes in a mass of ceramic material and ring to form a second assembly to mate with the rst assembly by insertion `into said detonation cavity;

forming a ceramic coating on one of said second pair of electrodes to tit into the socket of one of said first electrodes when the two assemblies mate, with a gap in the coating to form a spark chamber when the two assemblies mate;

abrading the electrodes to expose clean metal at said aap;

mating the two assemblies;

repeatedly applying voltage across the spark gap to test for the breakdown voltage;

and then placing explosive material in said detonation cavity against said second assembly.

8. A method of fabricating a detonation device of the character described, including the steps of:

installing a first electrode in a metal housing by means of ceramic and firing the ceramic to form a tirst assembly;

mounting a second electrode in a mass of ceramic material and firing the ceramic material to form a second assembly shaped and dimensioned to mate with the first assembly with a gap between the two electrodes to serve as a spark gap;

processing the two electrodes to expose clean metal after the firing operation;

and then mating the two assemblies.

9. A method of fabrication as set forth in claim 8 which includes the further steps of applying voltage across the two electrodes of the mated assembly to test the breakdown voltage at the spark gap.

No references cited.

EN A one end and a detonation cavity at the other end B J MIN A BORCHELT Pnmary Exammer P. A. SHANLEY, Assistant Examiner. 

1. A METHOD OF FABRICATING A DETONATION DEVICE OF THE CHARACTER DESCRIBED, INCLUDING THE STEPS OF: FORMING A FIRST ELECTRODE WITH A SOCKET IN ONE END; FORMING A SECOND ELECTRODE OF A CROSS SECTION TO TELESCOPE INTO SAID SOCKET WITH RADIAL CLEARANCE; MOUNTING THE FIRST ELECTRODE IN A FIRST MASS OF CERAMIC MATERIAL AND FIRING TO FUSE THE CERAMIC MASS TO THE ELECTRODE TO FORM A FIRST ASSEMBLY; MOUNTING THE SECOND ELECTRODE IN A SECOND MASS OF CERAMIC MATERIAL AND FIRING TO FUSE THE SECOND CERAMIC MASS TO THE SECOND ELECTRODE TO FORM A SECOND ASSEMBLY; FORMING A CERAMIC SLEEVE ON SAID SECOND ELECTRODE FOR SNUG FIT OF THE SECOND ELECTRODE INTO SAID SOCKET WITH A CIRCUMFERENTIAL GAP IN THE SLEEVE; ABRADING THE SECOND ELECTRODE AT SAID GAP TO EXPOSE CLEAN METAL; AND THEN MATING THE TWO ASSEMBLIES WITH SAID SECOND ELECTRODE TELESCOPED INTO SAID SOCKET. 